Increasing accumulation of recalcitrant organic plastics and other polymers in the environment has led to inquiries into how to make these materials more degradable. When discarded in the environment, many plastics are virtually indestructible by chemical or biological means normally available in a natural environment. Even though abrasive processes exist in natural environments, many plastics are so durable that hundreds or thousands of years may be required to appreciably reduce the volume of plastics currently in the environment. Hence, there is a need for polymers having sufficient reactivity so as to appreciably shorten their longevity after disposal.
As used herein, a "polymer" is a compound comprised of a continuous, more or less regular, covalently bonded sequence of the same or different structural unit, each type of structural unit, termed a "monomer," having a characteristic molecular structure and elemental composition. While most polymers have a molecular weight of at least 10000 daltons, certain "short" polymers, termed "oligomers," can have a molecular weight as low as about 1000 daltons and comprise only a few (less than 10) monomers. Vollmert, Polymer Chemistry, Springer-Verlag, New York (1973).
Reactive polymers are a new area of polymer synthesis and technology, having utility in a variety of technical applications, including catalysts and polymeric supports (see. e.g., Carraber, et al. (Eds.), Organometallic Polymers, Academic Press, New York, 1978), ion-exchange resins and perm-selective materials (Benham and Kinstle (Eds.), Chemical Reactions on Polymers, ACS Symposium Series 364, American Chemical Society, Washington, D.C., 1988), and selective chelating agents (see. e.g., Sheats, et al., Metal-Containing Polymeric Systems, Plenum Press, New York, 1985, pp. 355-366, 385-403, 425-455).
One subset of reactive polymers comprises photochemically reactive polymers. These polymers are of considerable interest because they are potentially useful as degradable plastics, photoresists (see. e.g., Zeldin, et al., (Eds.), Inorganic and Organometallic Polymers, ACS Symposium Series 360, American Chemical Society, Washington, D.C., 1988, chapters 2 and 16), and precursors for ceramic materials (id., chapters 2 and 10; Yajima, Ceramic Bull. 62:893 (1983)).
Unrelated studies of certain organometallic compounds that comprise carbonyl-containing metal--metal bonded "dimers" (bilaterally symmetrical molecules each comprising a single metal--metal bond crossing the axis of symmetry) have indicated that the metals participating in such bonds appear to be from groups VIB, VIIB, and the first (Fe) column of group VIIIB of the Periodic Table. Meyer and Caspar, "Photochemistry of Metal--Metal Bonds," Chem. Rev. 85:187-218 (1985). Nickel also forms such a "dimer." Metal--metal bonded dimers are photoreactive or "photo-labile," such terms denoting the tendency of the metal--metal bonds to photochemically disproportionate or fracture upon exposure to light. Studies of such compounds have heretofore been confined to the dimers in attempts to better understand photochemical reaction mechanisms. There are no known reports of useful polymers having been synthesized either from carbonyl-containing metal--metal bonded "dimers" or any other linkable compound ("monomer") containing a metal--metal bond.
But, there remains a need for photo-labile variants of recalcitrant polymers such as polyurethanes, polyesters, polyamides and other polymers that, at present, collectively pose a staggering disposal problem. Articles made from such photo-labile polymers should self-destruct in an illuminated environment at a rate much faster than the degradation rate of the corresponding polymers that are used presently.